This invention relates to electronics, and more particularly to noble metal compositions useful for producing conductor patterns adherent to substrates.
Conductor compositions which are applied to and fired on ceramic dielectric substrates usually comprise finely divided noble metal particles and inorganic binder particles, and are commonly applied to substrates using so-called "thick film" techniques, as a dispersion of inorganic powders in an inert liquid medium or vehicle. The metallic component of the composition provides the functional (conductive) utility, while the inorganic binder (e.g., glass, Bi.sub.2 O.sub.3, etc.) bonds the metal particles to one another and to the substrate. Thick film techniques are contrasted with "thin film" techniques, which involve deposition of particles by evaporation or sputtering. Thick film techniques are discussed generally in "Handbook of Materials and Processes for Electronics" C. A. Harper, Editor, McGraw-Hill, N.Y., 1970, Chapter 12.
Martin U.S. Pat. No. 3,293,501 discloses the manufacture of conductive films of noble metals plus copper glasses. Buck U.S. Pat. No. 3,776,769 discloses conductor compositions (which are fired in reducing atmospheres) of noble metal, 1-50% copper or its oxide(s), and vitreous binder. The necessity of firing in an atmosphere other than air is a distinct commercial drawback. Finally, Short U.S. Pat. No. 3,350,341 discloses silver compositions comprising a PbF.sub.2 -containing glass.
Glass-containing gold compositions presently available often contain large amounts of glass binder, which interferes with beam lead repair (beam leads are wires attached to conductor patterns on a substrate).
Noble metal conductor compositions employing a glass-free binder include the following. White U.K. Pat. No. 855,625, relates to the use of compositions of, e.g., silver plus copper oxide plus a minor proportion of a third "inert" material capable of being wetted by molten silver and copper oxide. The inert material may be alumina, magnesia, zirconia, titania, chromic oxide, or alumina-silicate. The firing temperatures are above 940.degree. C., preferably between 1000.degree.-1100.degree. C. No "inert" material which melts at the firing temperature is suggested. Glass-free conductor compositions of silver plus copper oxide have been an article of commerce for at least 15 years, and of gold plus copper oxide for more than 6 years. Gucker et al., Am.Ceram.Soc.Bull. 46, 789 (1967) disclose conductor compositions of gold and copper oxide. Smith U.S. Pat. Nos. 3,799,890 and 3,799,891 disclose glass-free gold conductor compositions using a copper oxide binder, and in 3,799,891, cadmium oxide also. Sheard U.S. Pat. No. 3,763,409, discloses capacitor electrode compositions including those of palladium or palladium oxide and copper or copper oxide.
Glass-free gold conductor compositions, although they may require smaller amounts of binder than conventional glass-bonded compositions, often must be fired at higher temperatures than the glass-bonded systems to achieve similar adhesion levels. Furthermore, gold/copper oxide compositions require chemical cleaning prior to thermal compression bonding.
There is a need in the electronics industry for gold conductor compositions comprising small amounts of binder, but which can yield good adhesion at low firing temperatures. The fired conductor should accept thermal compression binding readily, preferably without chemical precleaning, and should also permit beam lead repairs.